Fin for a reversible heat exchanger

ABSTRACT

A sheet of material defining a pair of parallel opposed edges adapted to be positioned generally transverse to the direction of airflow through the exchanger, said sheet of material having a plurality of corrugations therein extending parallel to the edges and a plurality of openings therethrough for receiving fluid conduits therein, and a portion of said sheet of material adjacent said opposed edges extending at an angle, relative to a plane including the sheet of material, greater than zero and less than 45*, such that for any given set of conditions for the heat exchanger (including rate of airflow, number of fins per inch, etc.) the exchanger is reversible in the airflow, without inflicting a loss in the heat transfer or an increase in the pressure differential across the exchanger, and the air deflection at the outlet of the exchanger is approximately zero in either direction.

United States Patent [151 3,645,330

Albright et al. Feb. 29, 1972 [54] FIN FOR A REVERSIBLE HEAT EXCHANGER [72] Inventors: John D. Albright, Minnetonka; Raymond J. Myers, Wayzata, both of Minn.

[73] Assignee: McQuay, Inc., Minneapolis, Minn.

[22] Filed: Feb. 5, 1970 [21] Appl. No.: 8,912

[52] US. Cl. ...l65/1Sl, 165/181 [51] Int. Cl ..F28d 1/00 [58] FieldoiSearch ..l65/151-153, 181,

[56] References Cited UNITED STATES PATENTS 1,920,313 8/1933 Mautsch ..165/15l 2,032,065 2/1936 Modine 165/151 3,443,634 5/1969 Pasternak. .....l65/182 3,515,207 6/1970 Lu ..165/l5 l Primary Examiner-Frederick L. Matteson Assistant ExaminerTheophil W. Streule AttorneyMerchant & Gould [57] ABSTRACT A sheet of material defining a pair of parallel opposed edges adapted to be positioned generally transverse to the direction of airflow through the exchanger, said sheet of material having a plurality of corrugations therein extending parallel to the edges and a plurality of openings therethrough for receiving fluid conduits therein, and a portion of said sheet of material adjacent said opposed edges extending at an angle, relative to a plane including the sheet of material, greater than zero and less than 45, such that for any given set of conditions for the heat exchanger (including rate of airflow, number of fins per inch, etc.) the exchanger is reversible in the airflow, without inflicting a loss in the heat transfer or an increase in the pressure differential across the exchanger, and the air deflection at the outlet of the exchanger is approximately zero in either direction.

9 Claims, 9 Drawing Figures PATENTEDFB29 I972 SHEET 2 OF 2 \l} f ('0 g V} T INVENTORS- JOHN 0. ALBR/GHT ;n 0A/D J. MYERS W ATTORNEYS o REMEQ 5mm cow Q QNvHY 3mm oo9 FIN FOR A REVERSIBLE HEAT EXCHANGER BACKGROUND OF THE INVENTION Field of the Invention:

The present invention applies specifically to the type of heat exchanger including a plurality of generally parallel fluid conduits connected to conduct a fluid medium, such as water or the like, and engaged through a plurality of generally parallel, spaced apart fins extending perpendicular to the conduits and especially to fins having severe undulations or waves therein. The fins and conduit are mounted in a tubular housing so that air or the like, upon being forced through the housing, contacts the fins and the conduits and exchanges heat, by giving up heat thereto or accepting heat therefrom. Such heat exchangers and housings are typically utilized in air conditioning units, industrial process equipment, etc. During installation, because of inadvertence or changed job conditions, it is not uncommon to reverse the position of the heat exchanger within the tubular housing, thereby, reversing the direction of airflow through the exchanger. Such a reversal of position generally radically changes the characteristics of the heat exchanger, thereby, substantially lowering the efficiency, and in some cases, rendering it impractical.

Description of the Prior Art:

It is well known in the prior art that fins of heat exchangers, which are constructed so that air is free to flow in a straight line therebetween, are extremely inefficient and provide a relatively low heat transfer. Because of this straight line flow, air immediately adjacent a fin, called a boundary layer, flows somewhat slower than air between the boundary layers due to resistance at the surface of the fins to air flow thereacross. This flowing of air through the exchanger in layers is known as laminar flow and reduces the heat transfer substantially.

Some prior art devices attempt to break up the laminar flow by creating turbulence in the air as it flows through the heat exchanger. One such prior art device is described in US. Pat. No. 1,557,467, entitled Radiator," issued to A. B. Modine on Oct. 13, 1925. Modine discloses fins for a radiator wherein corrugations and other irregularities are provided to create turbulence in air flowing between the fins. However, because Modines heat exchanger is utilized as a radiator in automobiles and the like, the amount of deflection of air at the outlet is not important and he simply terminates each of the fins in one of the hollows or grooves of the corrugations so that air leaving the heat exchanger is deflected downwardly at an angle of approximately 45. Further, Modine describes a turned-over leading edge to provide strength and a pleasing appearance. This turned-over leading edge will greatly reduce the airflow through the heat exchanger as larger numbers of fins per inch are utilized. Further, if the heat exchanger is reversed the turned-over edge will produce a relatively large pressure differential across the heat exchanger as larger numbers of fins per inch are utilized. Thus, Modines device is not reversible and causes an amount of air deflection at the outlet which is intolerable where heat exchangers are utilized in tubular housings, as in the presently described field.

SUMMARY OF THE INVENTION The present invention pertains to fin construction for a reversible heat exchanger wherein the fin includes a piece of sheet material defining a pair of opposed edges extending generally transverse to the direction of airflow through the exchanger with a plurality of corrugations formed between the edges and a plurality of corrugations formed between the edges and a plurality of apertures through the material for receiving fluid conduits therethrough and said piece of material further defining longitudinally extended edge angle portions adjacent each of said opposed edges anddisposed at an acute angle greater than zero degrees and less than 45 relative to a plane extending tangent to an adjacent corrugation and other like formed corrugations, said edge angle portions cooperating with edge angle portions of adjacent fins to provide an optimum amount of air deflection at the outlet and an optimum amount of differential pressure across the exchanger regardless of the direction of air flow through the heat exchanger.

It is an object of the present invention to provide improved fins for reversible heat exchanger whereby the characteristics of the heat exchanger are substantially identical in either direction of airflow.

It is a further object of the present invention to provide improved fins which produce optimum heat exchanger characteristics, such as air deflection at the outlet, pressure differential thereacross, heat transfer, etc., while rendering the heat exchanger reversible within an airflow.

These and other objects of this invention will become apparent to those skilled in the art upon consideration of the accompanying specification, claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings, wherein like characters indicate like parts throughout the figures:

FIG. 1 is a view in transverse section of an air duct showing an end elevation of a heat exchanger having the improved fins therein, portions thereof removed;

FIG. 2 is a sectional view as seen from the line 2-2 of FIG. 1, portions thereof removed;

FIG. 3 is an enlarged fragmentary sectional view as seen from the line 33 in FIG. 1;

FIG. 4 is an enlarged sectional view as seen from the line 4-4 in FIG. 2;

FIG. 5 is an enlarged view in transverse section of a sheet of material, prior to separation into a pair of improved fins;

FIGS. 6 and 7 are somewhat schematic views in transverse side elevation of prior art heat exchangers;

FIG. 8 is a semischematic view in transverse side elevation of the present heat exchanger including the improved fins; and

FIG. 9 is an approximate graphic representation of the outlet air deflection angle relative to the number of fins per inch in a heat exchanger utilizing the improved fins, with two different airflow rates specified.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings the numeral 10 generally designates a heat exchanger including a generally rectangularly shaped casing 11 having sidewalls l2 and 13 and upper and lower walls 14 and 15, respectively. A plurality of generally U-shaped conduits or tubes 16 are engaged through the sidewall 12, with the bight remaining on the exterior of the sidewall 12. The tubes 16 extend across the casing 11 in transversely spaced apart relationship and are engaged through the sidewall 13 with the two open ends of each of the tubes 16 extending a short distance to the exterior of the sidewall 13. A corresponding first open end of each of the tubes 16 is sealingly engaged in communication with a first header 17 mounted parallel with and exterior of the sidewall 13. The opposite corresponding open ends of each of the tubes 16 are sealingly engaged in communication with a second header 18 extending parallel with and exterior of the sidewall 13. The headers 17 and 18 have ports 19 and 20, respectively, for the ingress and egress of water or other heat-transferring fluid through the system.

The casing 11 is designed to be fitted into and form part of a tubular housing, such as air ducts 25 (illustrated in FIG. 2), although exchanges not associated with ducts are also included in this disclosure. The tubular housing or air ducts 25 direct air through the casing 11 and over the tubes 16 from one end 26 to the other end 27 of the casing 11. The normal airflow through the casing 11 from end 26 to end 27 is illustrated in FIG. 2 by the solid arrows. However, in some instances the direction of airflow withv respect to the heat exchanger 10 may be reversed so that the air flows from the end 27 to the end 26, as illustrated by the dotted arrows in FIG. 2, or the heat exchanger 10 may be installed in the air ducts 25 in a reverse direction. In either case the flow of air through the heat exchanger 10 is reversed.

A plurality of cooling or heating fins 30 are positioned in parallel spaced apart relationship between the sidewalls 12 and 13 of the casing 11 and in engagement with the tubes 16. Each of the fins 30 is formed from a piece of sheet material having good heat conducting characteristics, and the desired strength, durability, weight, ete., such as aluminum or the like. Each of the fins 30 is formed in a generally rectangular shape with opposed longitudinally extending edges 31 and 32 and two rows of longitudinally spaced apart openings 33 extending generally parallel with the edges 31 and 32 and spaced therebetween. The openings 33 in one of the rows are staggered or misaligned with the openings in the adjacent row for reasons which will become apparent presently. Each of the openings 33 has a generally cylindrical collar 34 extending outwardly from a side of the fin 30 generally coaxial with the associated opening 33. The outermost edge of the collar 34 is flanged outwardly at 35 to aid in assembly of the heat exchanger 10. In assembly, the tubes 16 are inserted through the openings 33 and a plurality of fins 30 are equally spaced thereon. The tubes 16 are then radially expanded by internal pressure or the like to firmly, frictionally engage the fins 30 and prevent relative movement thereof.

A plurality of longitudinally extending corrugations are formed between the edges 31 and 32 in each of the fins 30. In the present embodiment the corrugations are formed in a continuous sequence in a sheet of material and a piece of the material is removed along a specific line to form a fin 30. Referring to FIG. 5, which is a cross-sectional or end view of a sheet of material including two of the present fins 30, the sequence of corrugations can be seen. The sequence includes two corrugations 40 and 41, each having a generally sinusoidally shaped cross section or each including a rounded valley and hill. At one end of the two corrugations 40 and 41 a somewhat wider high area or hill 42 is formed and at the opposite end of the two corrugations 40 and 41 a somewhat wider low area or valley 43 is formed. The high area 42 has a small dip 44 at the center thereof to provide a double peak 45 and 46 configuration and the low area 43 has a small peak 47 at the center thereof to provide a double dip 48 and 49 arrangement. The sequence of two corrugations 40 and 41, a high area 42, two corrugations 40 and 41, a low area 43, two corrugations 40 and 41, a high area 42, continues across the sheet of material. To form a fin 30 from the sheet of material a piece is removed by cutting the sheet along the dips 44 of the high areas 42 and/or the peaks 47 of the low areas 43. As illustrated in FIG. 5, a row of openings 33 is positioned between adjacent high areas 42 and low areas 43. Thus, if a heat exchanger is to be constructed with a single row of openings 33, the pieces of material are severed from the sheet of material along each high area 42 and adjacent low area 43. In the present embodiment two rows of openings 33 are provided in each of the fins 30 so that the sheet of material is severed along the dips 44 in each of the high areas 42.

In the present embodiment the low portion of the dip 44 in the high area 42 and the high portion of the peak 47 in the low area 43 are separation portions or portions along which the sheet of material can be separated into fins 30. When the sheet of material is separated along either of these portions the angularly disposed portions forming the sides of the dip 44 and/or the peak 47 form edge angle portions 50 and 51, respectively. As illustrated in FIG. 5, the fins 30 are cut so that an edge angle portion 50 is adjacent each of the edges 31 and 32. In the present embodiment the dip 44 in the high area 42 and the peak 47 in the low area 43 are formed so that the edge angle portions 50 and 51 form an angle of approximately 17 with reference to a plane tangent to the peaks of the corrugations and to the dips of the corrugations, respectively. It has been found that an angle of between and for the edge angle portions 50 or 51 is optimum when nine or tens fins per inch are utilized with an air flow velocity of between 400 and 1,000 feet per minute.

Referring to FIG. 9, a graph illustrates the variations in deflection angle of the outlet air from the heat exchanger 10 (ordinate) for variations in the number of fins per inch (abscissa) and for variations of air velocity. In reviewing the graph of FIG. 9, it will be seen that the air flowing through the heat exchanger 10 has a tendency to follow the corrugations, for less than six fins per inch and, consequently, the air is deflected substantially in a first direction or the direction of the last corrugation. This corresponds somewhat to the prior art type of fins which simply stopped at the end of a corrugation, as shown in FIG. 6. In FIG. 6, the outlet and inlet edges are directed at an angle of approximately 45 to the plane of the fins and the deflection angle of the outlet air is so large as to be objectionable. This amount of deflection is intolerable in most heat exchangers utilized in the present field because it tends to create distortions in air distribution in the tubular housing or air ducts 25 rather than a uniform flow. Because of the large number of variables in the heat exchanger 10 and the system in which it is utilized, the actual angle of the edge angle portion 50 or 51 may vary between an angle greater than 0 and less than 45. As previously stated and illustrated in FIG. 9, for an edge angle portion 50 or 51 having an angle of approximately 17 degrees an outlet air deflection angle of approximately zero can be obtained with an air velocity of 400 to 1,000 feet per minute by installing between eight and ten fins per inch. Similarly, if any of the variables are altered, the angle of the edge angle portions 50 or 51 can be altered to return the outlet air deflection angle to approximately zero or the desired angle.

Referring to FIG. 7, heat exchanger fins are illustrated wherein the edges and the portions adjacent thereto are parallel to the air flow. This has been found to be undesirable because a laminar flow is set up at the inlet edge and adjacent parallel portions so that a relatively large differential pressure is produced between the inlet and outlet and the heat transfer is significantly reduced. Laminar flow development is retarded by the edge angle portions 50 or 51 of the present invention, so that the difi'erential pressure across the heat exchanger 10 is substantially reduced and a high heat transfer is maintained. FIG. 8 illustrates a semischematic view of a heat exchanger 10 incorporating the improved fins 30. A broken line 52 represents a plane extending tangent to the adjacent portion 45 or 46 and other like formed portions of corrugations 40 and 41. A dotted arrow 53 indicates generally the first direction of air at the outlet, which first direction is represented in the graph of FIG. 9 as negative. A second dotted arrow 54 indicates generally the second direction of air at the outlet, which second direction is represented in the graph of FIG. 9 as positive.

In general, the angle of the edge angle portions 50 or 51 should be adjusted so that the optimum desired outlet air deflection angle and differential pressure are obtained. While the angle of the edge angle portion 50 adjacent the edge 31 of the fin 30 may vary somewhat from the angle of the edge angle portion 50 adjacent the edge 32, in general these angles will be substantially equal since the various characteristics of the system in which the heat exchanger 10 is mounted remain equal. Further, to simplify manufacturing of the fins 30 the angles of the edge angle portions 50 adjacent each of the edges 31 and 32 should be substantially equal.

Because there is an edge angle portion 50 or 51 adjacent the inlet edge of each of the fins 30 to break up the laminar flow at the inlet of the heat exchanger 10 and because there is an edge angle portion 50 or 51 adjacent the outlet edge of each of the fins 30 to provide the correct air deflection at the outlet of the heat exchanger 10, the heat exchanger 10 is reversible within the air ducts 25 or the flow of air therethrough can be reversed. If desired, the edges 31 and 32 can be rippled to give added strength thereto, with little or no effect on the overall operation of the edge angle portions 50 or 51. The ripple is constructed so that the average angle of the edge portions 50 or 51 is the desired angle.

Thus, an improved cooling fin for heat exchangers is disclosed which is constructed so that the heat exchanger is reversible. Further, other characteristics of the heat exchanger, such as heat transfer, the pressure differential thereacross, etc., have optimum values while providing a desired or optimum outlet air deflection angle along with the reversibility. While a preferred embodiment has been described and illustrated, it should be understood that many variations, such s the type of corrugations, the direction of the angle of the edge angle portions, the spacing and positioning of the openings 33, etc., may be operatively incorporated into the structure.

We claim:

1. Fin construction for a reversible heat exchanger adapted to be positioned with opposite ends thereof in a flow of air, the heat exchanger having a plurality of generally parallel fluid conduits connected to conduct a fluid medium through the heat exchanger and a plurality of fins arranged in side-by-side relationship to dissipate heat from the fluid conduits by the flow of air, each of said fins comprising:

a. a piece of sheet material defining a pair of generally parallel, opposed substantially identical edges disposed adjacent the opposite ends of the heat exchanger and extending generally transverse to the direction of air flow through the exchanger;

b. a plurality of corrugations formed between said opposed edges and extending longitudinally with respect to said opposed edges;

c. a plurality of apertures formed in said sheet material between said opposed edges to provide a row of apertures extending longitudinally of said corrugations and adapted to one each frictionally receive one of the fluid conduits;

(1. said piece of material further defining longitudinally extended generally planar edge angle portions adjacent each of said opposed edges and disposed at acute angles greater than 0 and less than 45 relative to a plane extending tangent to an adjacent portion of a corrugation and other like portions of said corrugations;

e. said edge angle portions cooperating with edge angle portions of adjacent fins to deflect the air entering and leaving the heat exchanger whereby to create air turbulence at said edge angle portions and provide a heat exchanger having a heat transfer rate and a pressure differential between opposite ends thereof of a substantially equal amount regardless of the direction of air flow through the heat exchanger without deflecting air leaving the heat exchanger an excessive amount.

2. The structure of claim 1 wherein said apertures are formed in said sheet material to provide a plurality of spaced rows of apertures extending longitudinally of said corrugations, said apertures in each row of apertures adapted to frictionally receive one each one of the fluid conduits.

3. The structure of claim 2 wherein the piece of sheet material defines between adjacent rows of said apertures a separation portion extending longitudinally of said corrugations and in which said separation portion is flanked by said edge angle portions whereby separation of said sheet material along said separation portion provides a plurality of fins having said opposed edge angle portions.

4. The structure of claim 3 wherein said planar edge angle portions each extend from an adjacent corrugation at an acute angle relative to a plane lying tangent to said adjacent cormgation and other like formed corrugations.

5. The structure of claim 1 wherein said acute angle is between approximately 15 and 20.

6. The structure of claim 1 in further combination with means formed peripherally of each aperture of said fin for frictionally engaging a respective fluid conduit and spacing said fin from an adjacent fin.

7. The structure of claim 6 wherein said means formed peripherally of each aperture is a collar and in which each of said collars terminates in a radially outwardly flared end portion.

8. A heat exchanger adapted to be positioned in a tubular housing having a flow of air therethrough, said heat exchanger comprising:

a. a plurality of conduits adapted to conduct a fluid medium through said heat exchanger; b. a plurality of fins spaced transversely of said housing whereby air flowing in said housing passes between said fins, each of said fins comprising:

1. a piece of sheet material having opposite longitudinally extended side edges extending transversely of the tubular housing;

2. said opposite side edges defining corrugations therebetween which extend longitudinally and generally parallel to said side edges;

3. said fin having a plurality of openings formed therein between said opposite side edges and spaced longitudinally of said corrugations to fonn a row of openings adapted to frictionally engage one each one of said plurality of conduits;

4. a generally planar edge angle portion generally coextensive with and proximate each opposite side edge;

5. said edge angle portions cooperating with adjacent edge angle portions to deflect air passing through said heat exchanger a given angular amount as it leaves said heat exchanger relative to the direction of air flow through said heat exchanger whereby the heat transfer rate and the pressure ditferential between opposite sides of said heat exchanger, regardless of the direction of air flow through said heat exchanger, is approximately equal.

9. The structure of claim 8 wherein said edge angle portion is rippled. 

1. Fin construction for a reversible heat exchanger adapted to be positioned with opposite ends thereof in a flow of air, the heat exchanger having a plurality of generally parallel fluid conduits connected to conduct a fluid medium through the heat exchanger and a plurality of fins arranged in side-by-side relationship to dissipate heat from the fluid conduits by the flow of air, each of said fins comprising: a. a piece of sheet material defining a pair of generally parallel, opposed substantially identical edges disposed adjacent the opposite ends of the heat exchanger and extending generally transverse to the direction of air flow through the exchanger; b. a plurality of corrugations formed between said opposed edges and extending longitudinally with respect to said opposed edges; c. a plurality of apertures formed in said sheet material between said opposed edges to provide a row of apertures extending longitudinally of said corrugations and adapted to one each frictionally receive one of the fluid conduits; d. said piece Of material further defining longitudinally extended generally planar edge angle portions adjacent each of said opposed edges and disposed at acute angles greater than 0* and less than 45* relative to a plane extending tangent to an adjacent portion of a corrugation and other like portions of said corrugations; e. said edge angle portions cooperating with edge angle portions of adjacent fins to deflect the air entering and leaving the heat exchanger whereby to create air turbulence at said edge angle portions and provide a heat exchanger having a heat transfer rate and a pressure differential between opposite ends thereof of a substantially equal amount regardless of the direction of air flow through the heat exchanger without deflecting air leaving the heat exchanger an excessive amount.
 2. The structure of claim 1 wherein said apertures are formed in said sheet material to provide a plurality of spaced rows of apertures extending longitudinally of said corrugations, said apertures in each row of apertures adapted to frictionally receive one each one of the fluid conduits.
 2. said opposite side edges defining corrugations therebetween which extend longitudinally and generally parallel to said side edges;
 3. said fin having a plurality of openings formed therein between said opposite side edges and spaced longitudinally of said corrugations to form a row of openings adapted to frictionally engage one each one of said plurality of conduits;
 3. The structure of claim 2 wherein the piece of sheet material defines between adjacent rows of said apertures a separation portion extending longitudinally of said corrugations and in which said separation portion is flanked by said edge angle portions whereby separation of said sheet material along said separation portion provides a plurality of fins having said opposed edge angle portions.
 4. The structure of claim 3 wherein said planar edge angle portions each extend from an adjacent corrugation at an acute angle relative to a plane lying tangent to said adjacent corrugation and other like formed corrugations.
 4. a generally planar edge angle portion generally coextensive with and proximate each opposite side edge;
 5. said edge angle portions cooperating with adjacent edge angle portions to deflect air passing through said heat exchanger a given angular amount as it leaves said heat exchanger relative to the direction of air flow through said heat exchanger whereby the heat transfer rate and the pressure differential between opposite sides of said heat exchanger, regardless of the direction of air flow through said heat exchanger, is approximately equal.
 5. The structure of claim 1 wherein said acute angle is between approximately 15* and 20*.
 6. The structure of claim 1 in further combination with means formed peripherally of each aperture of said fin for frictionally engaging a respective fluid conduit and spacing said fin from an adjacent fin.
 7. The structure of claim 6 wherein said means formed peripherally of each aperture is a collar and in which each of said collars terminates in a radially outwardly flared end portion.
 8. A heat exchanger adapted to be positioned in a tubular housing having a flow of air therethrough, said heat exchanger comprising: a. a plurality of conduits adapted to conduct a fluid medium through said heat exchanger; b. a plurality of fins spaced transversely of said housing whereby air flowing in said housing passes between said fins, each of said fins comprising:
 9. The structure of claim 8 wherein said edge angle portion is rippled. 